Photoelectric grid emission

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Andrew Seltzman
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Photoelectric grid emission

Post by Andrew Seltzman »

I have observed that when running in glow mode, plasma containment will decrease and the poisser will become diffuse when the cathode grid heats up. This is probably due to excessive thermionic emission from the grid. On a deuterium fusor the plasma will emit a large amount of photons in the uv spectrum. In this case even if the grid is cool it may emit large amounts of electrons by the photoelectric effect.

If the grid (mainly iron) is plated with a metal with a higher work function, such as platinum, will this increase containment of deuterium plasma by decreasing photoelectric emissions?

Work function phi():
phi(iron) = 4.5eV
phi(platinum) = 6.35eV

Threshold wavelength LambdaT()

LambdaT(Fe) = 1240eVnm/4.5eV = 275nm
LambdaT(Pt) = 1240eVnm/6.34eV = 195nm

With the deuterium spectrum from 400nm-190nm (for ease of calculation, assume continuous distribution):

40.5% of the emitted light would be below the threshold wavelength for iron.
2.4% of the emitted light would be below the threshold wavelength for platinum.

By plating an iron grid with platinum the photoelectric emissions would be cut down to 6% of the initial level.

Andrew Seltzman
www.rtftechnologies.org/
Andrew Seltzman
www.rtftechnologies.org
Verp
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Re: Photoelectric grid emission

Post by Verp »

One of the experiments I wan to try when I build a fusor is to make central grids out of carbon fibers made by carbonizing different carbon containing compounds in a vacuum such as cotton thread or vinyl. I understand graphite can be useful in certain parts of tubes because it does not emit a lot of electrons and is good at absorbing the electrons it intercepts. I would think that carbon fibers would tend to emit a relatively few electrons under the working conditions in a fusor. I’m sure someone will speak up if they think otherwise. Another experiment I want to try is to see if there is a straightforward way to coat a metal fusor grid with pyrolytic graphite and see if that helps make it run better or longer. I’ve had people argue that ionized deuterium would tend to convert carbon into free hydrocarbon gasses in there, but it would guess that would be insignificant to the sheer amount of damage done to any type of grid as minute bits of it sputter away every time a high speed ion whacks into it and as its vapor pressure goes up as it gets hot.

Rod
Hector
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Re: Photoelectric grid emission

Post by Hector »

I would think that your highest source of secondary electron emission is the result of electron and ion bombarded of the cathode grid.

Hector
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